The present invention relates to an antilock braking system for a motor vehicle brake system having a wheel speed sensor and an electronic evaluation circuit which generates brake pressure control signals. The evaluation circuit includes a timing device that produces an increase of the brake pressure, for a time duration, with a large gradient, relative to the gradient over the entire time duration, and then with a smaller gradient. The time duration is a function of the length of the directly preceding pressure reduction.
An antilock braking system of this type is known from published German patent application OS No. 23 07 368, to which U.S. Pat. No. 3,888,550 corresponds. In this known system a deceleration signal which reduces the brake pressure is supplied to a timing element. When this deceleration signal is of greater length than the time constant of the timing element, a timing element with a long time constant is made effective in fixing the duration of the first pressure-buildup pulse, which then determines the length of the pressure buildup. If the pressure reduction was shorter than the first-mentioned time constant, a timing element with a shorter time constant becomes controlling in fixing the duration of the pressure-buildup pulse. Thus the duration of the pressure-buildup pulse is made a function of the duration of the preceding pressure reduction.
From published German patent application OS No. 24 60 904 to which U.S. Pat. No. 4,054,328 corresponds, it is further known to make the determination of the duration of the first pressure-buildup pulse, which produces a pressure buildup with a large gradient, a function of the duration of the pressure rise in the preceding control cycle rather than of the preceding pressure reduction. For example, when the pressure buildup with the small gradient is produced through several pulses, the sum of the pulses required is determined and allowance is made for that sum in fixing the duration of the first pressure buildup in the next control cycle.